The invention is based on a machine for filling and closing two-piece capsules as generically defined hereinafter. In a machine of this type known from German Auslegeschrift No. 11 17 471, the telescopingly joined bottoms and caps of the capsules are separated and transported with the caps in receptacles of a first conveyor wheel and the bottoms in receptacles of a second conveyor wheel. They are transported first to a monitoring apparatus, then to a filling apparatus and finally to a closing apparatus, where the caps are put onto the bottoms of the capsules. In the monitoring apparatus, the presence of the bottoms in the receptacles is checked by subjecting the receptacles placed to coincide with chambers in a test head below the conveyor wheel to negative pressure. If a capsule bottom is missing in any receptacle, then normal pressure prevails in the test head during the test period because of the ambient air flowing through the unoccupied receptacle, so that an electrical contact in an electrical control line drops, causing the machine to shut down. In this machine, purposeful scanning to find out which one of the predetermined number of receptacles on a conveyor wheel is unoccupied cannot be done.